This invention relates to a modification circuit for a telephone coin repeater. More particularly, it relates to a circuit adapted to provide improved coin detection and coin-free dialing for selected service codes and operator access in existing telephone coin repeaters without replacing the entire repeater. The telephone coin repeater, also known as an adapter, is normally an electromechanical device situated in the central office electrically coupled between the line feeder and access equipment in the central office. One of the purposes of the repeater is to detect the presence of a coin at a telephone pay station and, if a coin is present, to repeat the digits dialed in a form acceptable to the central office for switching through the call. An example of a coin repeater is disclosed in U.S. Pat. No. 2,835,738, issued May 20, 1958, and assigned to the General Telephone Laboratories, Inc., and U.S. Pat. No. 3,449,524, issued June 10, 1969, and assigned to Stromberg-Carlson Corporation. The disclosures set forth in these patents are hereby incorporated by reference.
One of the problems with existing electromechanical coin repeaters is their lack of versatility in providing coin-free dialing for selected service codes and operator access which many public utility commissions are now requiring.
Coin-free service has been provided by completely removing existing electromechanical repeaters and replacing them with an electronic circuit capable of providing these functions. However, this is a rather expensive way to provide a coin-free service, particularly since most of the relays and other equipment in the electromechanical repeaters are still viable circuits.
Another problem with existing electromechanical repeaters is that coin signals from pay stations were detected by a relay action. This type of arrangement is susceptible to false indications that a coin is present due to false ground and transient signals.
Another means for providing coin-free service has been to modify the pay station itself, however, it is obviously very expensive to modify each pay station rather than to modify the central office itself.